If it was a new iPhone then iTunes should have asked if you wanted to set it up or restore it from a backup, did it not do that? Re-attach the old phone and ensure that the 'backup to this computer' is ticked and wait for it to backup. Attach the 'new' phone and do a reset to factory settings, once finished you should be able to restore from the backup you just took. This all assumes that you had always synced the old phone with iTunes on that computer and that all of your apps, music etc. were on that ITunes.